The goal of this research is to elucidate the structural basis for both the enzymatic mechanism and RNA recognition by the RNA-modifying enzyme E. coli tRNA pseudouridine synthase I. Toward this goal we have determined the crystal structure of psuI apoenzyme at 1.5 E resolution. Recent experiments have demonstrated psuI diffracts to at least 1.2 E, though a full dataset could not be collectted due to time limitations. While our ultimate goal is to determine the structure of pusI in complex with tRNA, a high (1.2 E or better) resolution structure would be a valuable complement to the enzymatic studies as well as an asset for future studies of a psuI-tRNA complex.